Fuse system



June 24, 1952 R. B. BucHNER FUSE SYSTEM Filed Feb. 15', 1949 gin/n Qd SZ AAA Patented June Z4, 1952 FUSE SYSTEM Robert Bertold Buchner, Eindhoven, Netherlands, assigner to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application February 15, 1949, Serial No. 76,504 In the Netherlands April 26, 1948 This invention relates to a circuit-arrangement by which an electric signalling system. more particularly an automatic telephone system, is protected automatically. y

In such systems it is customary to connect the subscribers, divided into groups, to a common voltage supply and to protect the supply against short-circuits by separate fuses provided in the various groups. The groups are divided into subgroups in the same manner, and the sub-groups may, for example, be further divided into racks which, in turn, may be divided into selectors with associated relays. In each next following division stage the fuses used are smaller than in the previous stage. The groups and sub-groups are usually protected by so-called power current fuses, whereas feeble current fuses are used in the further division stages. The feeble current fuses may be provided with an alarm contact which is closed upon blowing of the fuse, due to which an alarm device is operated and an alarm lamp is lit for indicating and localizing the defect.

In conventional circuit arrangements a blown power current fuse is signalized by means of an alarm relay which is supplied with current via the fuse in question and is normally energized. As soon as the fuse or a fuse in a preceding division stage is blown, the relay is de-energized and alarm is given.

The conventional safety arrangements are not very effective. In practice, it repeatedly occurs upon overloading that a feeble current fuse does not melt immediately, due to which a less sensitive power current fuse might be blown earlier than a feeble current fuse so that the number of user groups disturbed would be greater than is necessary. Furthermore, a fuse may finally be blown after continued loads.

In the majority of cases a short-circuit occurring will be of a very short duration. For instance, a dropping wire may cause a wrong contact to be made during operations in the exchange. In this event a short-circuit occurs, due to which one or more fuses may be blown, but the next instant the short-circuit is again removed. If a voltage were again present at this instant the telephone traiiic could again proceed normally.

The present invention meets these disadvantages and it exhibits the feature that at least one of the fuses is shunted by a circuit comprising the series-connection of an alarm relay and a fuse.

By this expedient it is achieved that. if the first-mentioned fuse is blown, the subscribers sup- 9 Claims. (Cl. 177-311) plied via the fuse may still receive current through the series-connection of the alarm relay and the second fuse, by which the alarm relay is energized. In the event of a short-circuit of short duration the second fuse will quite likely remain intact so that the telephone traflc may proceed normally.

In order that the invention may be clearly understood and readily carried into effect it will now be explained more fully with reference to the accompanying drawing, which represents diagrammatically the supply portion of a telephone exchange.

The subscribers supplied by the common battery Ba are divided into a number of main groups, of which only groups A and B are shown in the drawing. Each main group is subdivided into a number of sub-groups (a. b) and each sub-group is divided in the same manner into racks which, in turn, are divided into subscribers per selector. At every sub-division the supply current is split up into a number of branches which are protected by separate fuses.

The main groups A and B are fed via power current fuses SA and SB respectively of, say, 15 amps, one end of these fuses being connected to the negative terminal of battery Ba. The other ends of the fuses are each connected through the series-connection of a fuse (SIA and S113 respectively) and a resistance (RA and RB respectively) to one end of a winding HA1 of an alarm relay HA which is common to the main groups A and B. The other end of the winding is connected, through a power current fuse of, say, 20 amperes, to the common ends of the fuses SA and SB and to the negative terminal of the battery.

The resistance of the relay winding in series with RA or RB has a high value with respect to the resistance of the fuses SA and SB, so that only a small fraction of the feed currents of main groups A and B traverses the winding HA1. This fraction is further reduced, since the winding HA1 is shunted by a resistance RAB.

If the fuse SA is blown, the main group A is supplied with current via the by-path constituted by the fuse SAB, the parallel-connection of winding HA1 and resistance RAB, resistance RA and fuse 51A. At first, the supply current mainly traverses RAB only, since the current traversing the relay winding does not directly attain its full value due to self-induction. The resistance RB has a high value with respect to the resistance of the parallel-connection of the winding and RAB, so that only a small part of the supply current of main group A traverses` the fuse Se.

Vcomes operative.

3 Consequently, the latter is not appreciably loaded additionally. The same may be achieved by substituting rectiiiers for the resistances RA and RB.

The relay HA is now energized and completes by way of its make contact HAi, the second winding HAz and the feeble current fuse S1, a holding circuit for itself, and at the same time the alarm lamp Li is lit to indicate the group in which the defect occurs. Furthermore, an acoustic alarm device is made operative by way of contacts (not represented).

If the blowing of SA is due `to a short-circuit of short duration, delayed blowing of a feeble current fuse or continued heavy loads of the fuse, the fuse SlA need not be blow-nafter the inse SA has melted, and group A may be further supplied without interruption of the `telephone trailic.

In the event of a continued short-circuit, S1. will naturally also be Yblown and group 'A 'no longer passes current. Prior tothisfhowever, the alarm relay operates.

In the circuit-'arrangement represented the defect signalization'of a powercurrcnt fusein the main grou is is catered for by an Aalarm relay. Naturally, each of these relays may-alternatively operate more than two main groups.

The'same circuit-'arrangement'is'used for protecting the sub-groups. Thus, for instance, an alarm relay is-added to the sub-groups "a and b of main group A.

The feed circuits of the holding windings of the alarm relays of mainand sub-groupscomprise feeble current fuses S1 and Sz respectively of, say, 1 amp. These fuses -are lfurnished with an alarm contact S11 and S12 respectively which is closed when the fuse is blown. If fuse S2 is blown, a circuit from earth, make contact S12, resistance R2, winding HAz-of the alarm relay of a main group, feeble'current fuse Si `tothe negative terminal of the battery, is completed by the closure-ofcontactSlz. Owing to this, the relay HA is'energizedand the alarm devicebe- 4To localize the defect one or more-alarm ylamps'Lz (which may lbe fitted Ato several division panels) may be lit. The resistancesRi and 'Re are-chosen to be such that-the lamp L1 does notblink on closing S12.

Similarly, a-defective fuse S1,-due to which contact S11 is closed, is signalized by means'of the alarm-relay HA of a'sub-group.

What I claim is:

1. In an electric signalling system, a supply line including a main fuse, a voltage source-connected to said line, and an alarm circuit coupled to said fuse, said circuit including-a relay having an energization winding and a switch actuated thereby, an auxiliary fuse connected in-series with said winding across said mainfuse whereby in the event said'main fuse blows, the voltage-is suppiied to said line through said auxiliaryfuse and said winding, thereby energizing saidwinding, and means responsive to the actuation ofsaid switch to produce an alarm indication.

2. An arrangement, as set forth in claim 1, wherein said relay further includes a holding windingconnected'through said switch tosaid source whereby upon actuation of saidswltch said holding winding is energized and retains said switch in its operative position.

3. An arrangement, as set forth in claim 1, wherein said indicating means-is constituted'by anincandescentdevice connected'- in series with said switch to said source.

4. In an electric signalling system, a plurality of supply lines each including a main fuse, one of the ends of the main fuses in said lines being interconnected, a common voltage source connected through said interconnection to each of said lines, and an alarm circuit coupled to two of said lines and including a. relay having an energization winding and a switch actuated thereby, rst and second resistances, an auxiliary fuse connected in series with said winding and the first resistance across the main fuse in one of the two lines, said auxiliary fuse being also connected in series with said winding and said second resistance across'the main fuse in the other of said two lines, and means responsive to the actuation of said switch toproduce an alarm indication.

5. Inan lelectric signalling system, a plurality of supply lines each including a main fuse, a common voltage source connected to each of said lines, and an alarm circuit coupled to two of said lines and including a relay having an energization winding, a switch actuated thereby and a holding winding, iirst andsecond resistances, an auxiliary use connected through said energize.- tion winding and said rst 'resistance'acrossthe main fuse in one of'said two lines, said auxiliary fuse being connected through said .energization winding and said `second resistance across the main fuse in the other of said two lines, said holding winding being connected through said switch to'said voltage source, and a'lightindicator connected through said switch Vto said voltage source.

6. An arrangement, assetiorth in claim 5,'further including aresistor shunted across said energization winding.

7. An arrangement, as set .forth in claim 6, wherein said auxiliary Afuses ,possess a higher power rating than said main fuses.

8. An arrangement, as set forth in claimv '7,Iurther including a pair of additional vfuses interposed between said main fuses in the two lines and said first and second resistances, respectively.

9. In an electric signalling system, aplurality of supply lines each including a mainfuse, a common voltage source connected to each .of said lines, and an. alarm circuit coupledto two .ofsai'd lines and including a relay having vanenergization winding, a switch actuated therebyand a holding winding, rst and .second rectiers, Van auxiliary 1fuse connected through Ysaid venergization windingand said first rectifier across the main fusein one of said two .lines,.said.auxiliary ,fuse being connected Vthrough .said energization winding and said secondrectifieracross .the main fuse in the other of saidtwo lines, saidholding winding being connected through. said switch-to said voltage source, .and a lightindicatorconnectedthroughsaid switch to-sai'd vvoltage source.

ROBERT BERTOLD .BUCHNER REFERENCES CITED The following references are of recordfin the iile of this patent:

UNITED STATES PATENTS Number Name 'Date 439,392 Edison Oct. 28, 1890 '2,317,030 VColvin Oct.`20, 1943 2,414,932 Crockett -Jan.. 28, 1947 FOREIGN PATENTS Number Country TDate A720,500- `France Feb.-19, 1932 

